Welding Tips and Tricks

If anyone has followed my NDT topic under "project", you know what I work on, and may recognize the cause of this:
Major fail... there's a second crack, near the bearing block, if you look.

Steve S

Is this from the trailer you suspect was in a collision? I wonder what the speed limit is at their yard? Ours is 10 mph, but I work with building materials, not liquid hydrogen! Haha.

You do some fascinating work Otto and I enjoy learning from your post.

This one is a liquid Argon trailer. It's insulation includes being filled with perlite between the inner and outer jackets, as well as high vacuum. In the picture is a bearing block, that fits in a large plastic (PTFE family) bushing to hold it stationary. Near the front of the trailer is a similar block, only it's bushing has over an inch of extra room for front-to-back movement to allow the (aluminum) inner vessel to shrink when it get cold (loaded with liquid) and expand when it's warm (during maintenance and repair). It basically slides front-to-back.

The front bushings were not properly protected from perlite, became full, and wouldn't allow the bushings to move. The simple hot-cold expansion and contraction of the inner vessel, without freedom to move, tore this doubler loose. Literally tons of force.

The good news is I completed the inner vessel inspection this AM, and there's no internal damage. There are a couple minor repair issues, but none related to the damage in the picture. It's fortunate that these doublers (there are eight, total, four in back, four in front, at 3, 6, 9, and 12.) were the weak link, and perhaps they were designed that way.

I'm glad you enjoy the read... Not enough of us are blessed to enjoy their jobs enough to talk about them after work, other than b!tching in the bar.

Steve S

WOW! That really went!

Tons of force for sure! That's crazy. What process do you plan to use for the repair? I would think MIG, to retain the uniformity of all the doublers, but what do I know. Haha.

I love welding and love talking about it. Now, I just need to find a job in the field. Haha. Until then I'll keep practicing and learning from you guys.

Our shop procedure, specified by the client, is that any repair weld that involves the inner vessel (which is ASME code work) must be TIGged.

Fortunately, we have ready access to Helium, so I can custom-mix my gas as I use it, which makes these heavy sections MUCH easier.

There's a broad work scope on this project, though, unrelated to the damage, so it's possible they'll scrap it out once they see the estimate. These trailers, unlike the hydrogen trailers, can be replaced for about $300,000. This one's 30 years old, so anything over half the replacement will probably get it scrapped.

We'll see.

Steve S

I would imadgine if you did what was needed and it was under replacement cost or even the same price as another 30 year old trailer they would get it fixed because then it is just that much better...

I am comparing it to lets say getting a Stihl 880 chainsaw rebuilt for $400 and it will be "like new" or buying another the same age for $800 "as is" so that is the mindset I am in...

Peter.

The decision came in yesterday...

It's scrap. When the repairs were figured with the original work-scope, it's just more practical to replace it. Consider this trailer has a deisel-driven pump. The engine needed replaced, the entire driveline rebuilt, the cryo pump overhauled, and the entire suspension upgraded to air-ride w/ ABS, which requires replacing the entire bogie (rear subframe). Lighting upgrades to current standards. Plus comlete removal and replacement of the perlite insulation and accomanying vacuum work.

I think they made the wise choice.

They'll buy a brand-new one, with a warranty, for less than twice the repair cost on a trailer with 5 million miles on it. This client has Deeeeeep pockets.

Steve S